The present invention relates to an ink occlusion material for writing utensils, particularly to an aqueous-ink occlusion material and a method for the preparation thereof.
Previously known ink occlusion material for writing utensils, are prepared by (a) impregnating a precondensate of a thermosetting resin such as melamine, epoxy or phenol resin in a fiber bundle of synthetic fibers such as polyester, nylon, acrylic, vinylon or polyethylene fibers, and (b) compressing and heating the fiber bundle to adhere the synthetic fibers in order to form the fiber bundles into a shape. However, by using thermosetting resin in the occlusion material, it is necessary to smoothly apply a liquid such as an ink for writing utensils. As a result, the thermosetting resin does not adhere uniformly to the fiber bundle resulting in the capillary structure useful for ink flow and ink occlusion becoming incomplete and the fluctuation of ink flow increasing.
To improve such disadvantages, Japanese Patent Publication No. 37571 of 1975 discloses a method in which a mixed sliver of a plurality of fibers having different melting points is covered with a resin film having approximately the same melting point as them in order to effect hot melt adhesion. However, the disadvantage of this method is that the ink utilization ratio is lowered as the resin absorbs ink.
As an alternative method, Japanese Patent Publication No. 16963 of 1970 discloses a method in which the fibers are combined parallel in the axis direction. The resulting continuous fiber bundle is (a) treated with an adhesive solution, (b) squeezed and (c) the solvent is removed by drying in order to adhere and fix the fibers and (d) finally the periphery of the fiber bundle is covered with a polymer film in order to prepare an ink conclusion material. However, the disadvantage of this method is that the step of adhering the film at the overlapping portion after covering the bundle with the polymer film cannot be speed up, the percent defect is high and the resulting continuous fiber bundle is not economical.
Previously, in Japanese Patent Laid-open Publication No. 199698 of 1982, the present inventors proposed a method in which crimped acrylic fibers was combined parallel to the fiber axis direction and an organic solvent, which can dissolve the fibers applied is on the resulting fiber bundle. The bundle is heated to melt-adhere at least a portion of the fibers. However, this method, which the fibers are combined parallel to the fiber axis direction, has the disadvantage that the fibers partially fall out during the squeezing procedure involving th organic solvent and during the drying procedure. Moreover, the adhered spots are few unless the heating is carried out under compression. On the other hand, as the acrylic fiber becomes more hydrophilic such as polyester fiber, polyethylene fiber and polypropylene fiber, it retains more ink when an aqueous ink is used. Thus, the ink utilization ratio decreases.
Furthermore, Japanese Laid-Open Patent Publication No. 60774 of 1986 discloses a method in which a fiber of low hydrophilic nature such as polyester fiber is mixed in the fiber bundle in order to solve the problem of the above-mentioned Japanese Laid-Open Patent Publication No. 199698 of 1982. However, when polyester fiber, etc. is mixed uniformly, the ink utilization ratio can be somewhat improved but the ink retainability is lowed in order to get an enough ink utilization. However, the problem of fiber escape occurs.
An object of the present invention is to provide an ink occlusion material which has the same ink retention as in the case of using an acrylic fiber alone, while showing a high ink utilization ratio, giving no problem of fiber escape, which then can be easily handled. Another object of the present invention is to provide a easy method for the preparation of such an easily handled ink occlusion material for writing utensils at a commercial scale and at a low price.